The relationship between vital exhaustion, depression and comorbid illnesses in patients following first myocardial infarction
Introduction
Vital exhaustion, characterised by feelings of excess fatigue, lack of energy, irritability, and demoralisation, has been postulated as being a precursor of both fatal and nonfatal myocardial infarction (MI) in otherwise healthy individuals [1], [2], [3], [4]. This association between vital exhaustion and MI remains even after established cardiovascular risk factors (e.g., raised blood pressure and cholesterol, use of antihypertensive medication, and smoking) have been controlled. In addition, vital exhaustion has been found to be associated with sudden cardiac arrest and with adverse cardiac events in a group of successful angioplasty patients [4], [5]. The core symptoms of vital exhaustion are similar to those of depression, however, which can include reduced energy and increased fatigability, hopelessness, and irritability. Depression has also been shown to be a risk factor for the development and progression of cardiovascular disease [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18].
Studies examining the association between vital exhaustion and depression have failed to clarify how these factors are related. Kopp et al. found a moderate association between vital exhaustion and depression (r=.62) in a large, representative sample of the Hungarian population [20]. They also found that the dimensions of vital exhaustion and depression had different associations with risk factors for cardiac disease; depression was associated with hostility, negative health beliefs, alcohol and drug abuse, whereas vital exhaustion was associated with previous treatment for cardiovascular disease. Wojceichowski and colleagues confirmed the association between depression and scores on the Maastricht Questionnaire (MQ; vital exhaustion) in patients following their first MI, although factor analysis of the vital exhaustion and depression scores failed to reveal separate depression and fatigue factors [19]. Appels and colleagues, on the other hand, studying the findings from a large number of healthy men, found that vital exhaustion was composed of three factors: fatigue, depressive affect, and irritability [3]. Furthermore, the risk of subsequent MI was attributable to the fatigue dimension of vital exhaustion. In the only study to investigate the impact of both fatigue and depression following MI, depression predicted mortality post-MI until the effects of fatigue were controlled when the effects of depression become nonsignificant [14]. The effect of fatigue, therefore, may account for some of the variability in the findings of studies that have examined the impact of depression on cardiovascular outcome.
Vital exhaustion and depression are related constructs, although the nature of the association is complex. Previous research literature indicates that vital exhaustion and depression may be associated on a number of different levels. First, the similarity in the core features of vital exhaustion and depression suggest that they are different aspects of the same risk for poor cardiovascular outcome. Second, the risk of adverse cardiovascular outcome may arise from a common confounding characteristic such as preexisting cardiac disease or other significant comorbid illness. Such confounding factors would be expected to predict depression, excessive fatigue, and poor prognosis following MI. Third, depression and vital exhaustion may be separate constructs and represent independent risk factors for cardiac disease, which may occur together at times. Separating the risks associated with vital exhaustion and depression has been complicated, however, by the fact that the main measure of vital exhaustion (the MQ) records symptoms that reflect both depression and vital exhaustion; that is, it has poor content validity.
We have performed a detailed cross-sectional assessment of demographic, biological, and psychological variables in a large representative sample of patients admitted to hospital following their first MI. We aimed to investigate the degree of association between depression and vital exhaustion in our sample. In addition we aimed to investigate whether this association was attributable to the confounding influence of comorbid illnesses or due to the overlap of assessments of depression and vital exhaustion, i.e., the result of poor content validity of the measures used. Thus, the underlying structure of the MQ (which measures vital exhaustion) was explored. The specific hypotheses tested were that (1) vital exhaustion and depression scores would be highly intercorrelated and (2) the association between vital exhaustion and depression could, in part, be attributed to the confounding influence of preexisting, comorbid illnesses.
Section snippets
Sample
Consecutive patients with suspected MI admitted to four inner-city hospitals in the UK were screened for this study. Subjects were considered for inclusion if (i) they were less than 80 years of age, (ii) they had no history of previous MI, (iii) their MI was not related to the performance of an invasive medical procedure (e.g., angioplasty), and (iv) they met WHO criteria for MI [21]. These criteria required that two of the following features were present: (i) history of typical chest pain,
Results
Baseline characteristics of the population studied are presented in Table 1. Comorbid illnesses were common in our group, the commonest being rheumatological disorders (n=98, 32% of patients), hypertension (n=76, 25%), respiratory disorders (n=47, 15%), abdominal/bowel complaints (n=38, 13%), and diabetes (n=21, 7%). Only 31 subjects (10%) were known to suffer from cardiovascular disease prior to their MI. The majority of subjects were assessed as Killip Class I following MI (no signs of
Factor analysis of the vital exhaustion scores (MQ)
Items scores for the MQ were subjected to factor analysis. Table 2 shows the rotated factor structure. Four distinct factors (i.e., eigenvalues ≥1) emerged, which explained 53.7% of the total variation. The two main factors accounted for 18.2% and 17.9% of the variance, with the two others accounting for 9.5% and 8.1% of the variance. Items from the MQ that loaded on these factors (loadings >.4 only) are also shown in Table 2. The largest factor consisted predominantly of items from the MQ that
Discussion
This is the one of two studies that assessed the relationship between depression and vital exhaustion in a large sample of MI patients. This is the first, we believe, to have to controlled for age, sex, and number of comorbid physical illness, which are clearly associated with vital exhaustion.
We found that vital exhaustion scores were significantly associated with both the depression and anxiety scores of the HADS, and that the magnitude of these associations remained when the influences of
Acknowledgements
This study was funded by UK Medical Research Council and British Heart Foundation.
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